High density phase-change type optical disk having a data efficiency of more than 80 percent

ABSTRACT

An optical disk includes a land and a groove. On this optical disk, data is recorded on both the land and the groove. A distance between the center of the land and the center of the groove adjacent to the land is 0.28 μm or more. The optical disk has a data efficiency of 80% or more. Thus, an optical disk having a storage capacity of 25 GB or more can be provided.

BACKGROUND OF THE INVENTION

The present invention relates to a disk storage medium on which data isrecorded by light (which will be referred to as an “optical disk”).

In recent years, optical disks such as DVD-RAM and DVD-RW have been usedas storage media for recording digital information thereon at a highdensity. Each of these optical disks used commonly today is designed insuch a manner as to record data of 4.7 GB per side by being irradiatedwith a laser beam having a wavelength of 650 nm through an opticalsystem (e.g., objective lens) having a numerical aperture of 0.6. Thus,approximately one hour of video signal can be recorded on each side.

However, the maximum recordable length of approximately one hour is notlong enough to cope with most of actual applications. Accordingly, tomake those optical disks as handy as home video tape recorders, thoseoptical disks should acquire an even greater storage capacity. Also, toperform editing and other types of operations by making full use of therandom-access capability, which is one of advantageous features of theoptical disks, video signal needs to be recorded for about five hours ormore. In that case, the data storage capacity of the optical disksshould be at least 23 GB and preferably more.

However, it is not easy to produce an optical disk with such a hugecapacity because the recording density must be tremendously increasedfrom the currently available one.

The present invention overcomes the problems described above, and aprimary object thereof is to provide an optical disk that achieves ahigh recording density and a huge storage capacity.

BRIEF SUMMARY OF THE INVENTION

An optical disk according to the present invention includes a land and agroove. On the optical disk, data is recorded on both the land and thegroove. A distance between the center of the land and the center of thegroove adjacent to the land is 0.28 μm or more. And the optical disk hasa data efficiency of 80% or more.

In one preferred embodiment, the data is recorded by using a modulationcode of a 3T system.

In another preferred embodiment, the data is recorded by using amodulation code of a 2T system.

In another preferred embodiment, a product code is used as an errorcorrection code.

In another preferred embodiment, the groove is wobbled.

In another preferred embodiment, the optical disk further includes alight transmitting layer on the surface of the disk on which the grooveand the land have been formed. The light transmitting layer has athickness of 0.2 mm or less.

Another optical disk according to the present invention includes a landand a groove. On the optical disk, data is recorded on either the landor the groove. A pitch of the groove and a pitch of the land are 0.32 μmor more. And the optical disk has a data efficiency of 80% or more.

In one preferred embodiment, the data is recorded by using a modulationcode of a 3T system.

In another preferred embodiment, the data is recorded by using amodulation code of a 2T system.

In another preferred embodiment, a product code is used as an errorcorrection code.

In another preferred embodiment, the groove is wobbled.

In another preferred embodiment, the groove includes a plurality ofwobble patterns.

In another preferred embodiment, the wobble patterns represent addressinformation.

In another preferred embodiment, the optical disk further includes alight transmitting layer on the surface of the disk on which the grooveand the land have been formed. The light transmitting layer has athickness of 0.2 mm or less.

In another preferred embodiment, the optical disk has a storage capacityof 23 GB or more.

In another preferred embodiment, the optical disk further includes arecording layer of a phase change material and the data is rewritable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments of the invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustrating the invention, there is shown in the drawings embodimentswhich are presently preferred. It should be understood, however, thatthe invention is not limited to the precise arrangements andinstrumentalities shown.

In the drawings:

FIGS. 1(a) and (b) are respectively a perspective view and a partialview illustrating an optical disk according to a first embodiment.

FIG. 2 is a schematic representation illustrating an optical disk drivefor performing read and write operations on the optical disk of thefirst embodiment.

FIG. 3 is a graph showing the respective storage capacity versus jittercharacteristics of a modulation code (1, 7) of a 2T system and amodulation code (8-16) of a 3T system.

FIG. 4 is a graph showing the respective storage capacity versus errorrate characteristics of a modulation code (1, 7) of a 2T system and amodulation code (8-16) of a 3T system.

FIG. 5 is a graph showing, in comparison, the correcting abilities of aproduct code (PC) and a long distance code (LDC).

FIG. 6 is a diagram illustrating exemplary diagonal interleavingprocessing on a product code.

FIGS. 7(a) and 7(b) are respectively a perspective view and a partialview illustrating an optical disk according to a second embodiment.

FIG. 8 is a graph illustrating a track pitch versus push-pull signalamplitude variation characteristic.

FIGS. 9(a) and 9(b) are graphs showing how the jitter and the bit errorrate of a PRML read signal change with the tilt angle when a modulationcode of a 2T system is used:

FIG. 9(a) is a graph associated with a tangential tilt; and

FIG. 9(b) is a graph associated with a radial tilt.

FIGS. 10(a) and 10(b) illustrate four types of wobble patterns of trackgrooves:

FIG. 10(a) illustrates the pattern primitives; and

FIG. 10(b) illustrates specific wobble patterns.

FIG. 11 illustrates a main part of an apparatus for use to readinformation from the disk of the second embodiment.

FIG. 12 illustrates a groove of the disk and a wobble signal and a pulsesignal that have been generated therefrom.

FIG. 13 illustrates an exemplary configuration for a circuit forgenerating the pulse signal and a clock signal from the wobble signalshown in FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

Embodiment 1

FIGS. 1(a) and 1(b) are respectively a perspective view and a partialview of an optical disk 1 according to a first embodiment of the presentinvention.

As shown in FIG. 1(a), spiral grooves 2 have been formed on the opticaldisk 1. This optical disk 1 has a diameter of 120 mm and has been formedto have a total thickness of 1.2 mm. Also, as shown in FIG. 1(b), theoptical disk 1 is made by forming an information recording layer 4 of aphase change material such as a GeSbTe film, for example, on a disksubstrate 3. A light transmitting layer 5, which transmits a laser beamand guides it onto the information recording layer 4, is further formedon this information recording layer 4 so as to have a thickness of about0.1 mm. A zone between two grooves 2 is called a land 6. In this opticaldisk 1, data is recorded on both the grooves 2 and the lands 6.

As can be seen from FIG. 1(b), the grooves 2 are wobbled. It should benoted that the optical depth of the grooves 2 is set approximately equalto λ/6, where λ is the laser wavelength. This is done to reduce thecrosstalk occurring between the land 6 and the grooves 2.

Next, an optical disk drive 800 that can write or read informationon/from this optical disk 1 will be described with reference to FIG. 2.

The optical disk drive 800 includes a semiconductor laser diode 802 foremitting a laser beam. The laser beam, emitted from the semiconductorlaser diode 802, passes through a collimator lens 803 and a beamsplitter 804 and then is focused by an objective lens 805 onto theinformation recording layer of the optical disk 1.

In performing a write operation, the optical disk drive 800 changes theintensity of the light beam, thereby writing information on therecording layer of the optical disk. On the other hand, in performing aread operation, the optical disk drive 800 receives the light, which hasbeen reflected and diffracted by the optical disk 1, at a photodetector807 by way of the objective lens 805, beam splitter 804 and condenserlens 806, thereby generating read signals based on the light received.The photodetector 807 includes a plurality of light-receiving elementsA, B, C and D, for example. In accordance with the quantities of lightthat have been detected by these light-receiving elements A, B, C and D,a read signal computing means 808 generates the read signals.

The read signal computing means 808 sends out a focus error (FE) signaland a tracking error (TE) signal to a focus control means 809 and atracking control means 810, respectively. These control means 809 and810 appropriately drive an actuator 811 for moving the objective lens805 in response to the FE and TE signals, thereby irradiating a desiredtrack location with a light spot of the focused light.

Also, this optical disk drive 800 reads out the information stored onthe optical disk 1 by using the light spot that has been subjected tothe focus and tracking controls. In accordance with RF and TE signals,which are among the output signals of the read signal computing means808, an address detecting means 812 detects the address.

The following Table 1 shows various design parameters of the opticaldisk 1 of this embodiment, the wavelength of the laser beam for use torecord information on this optical disk, and the numerical aperture ofthe objective lens for use to focus the laser beam onto the opticaldisk:

TABLE 1 Laser wavelength 405 nm Numerical aperture 0.85 of objectivelens Thickness of 0.1 mm light transmitting layer Diameter of disk 120mm Data recording area 24-58 mm in radius Data efficiency 83.7%Recording method Land/groove recording Track pitch 0.294 μm Data bitlength 0.1213 μm Channel bit length (T) 0.0606 μm Shortest mark length3T (0.1819 μm) Error correction code RS (208, 192, 17) × RS (182, 172,11)

As shown in Table 1, the optical disk 1 of this embodiment is designedin such a manner that information is recorded by an optical disk drivethat uses a laser beam with a relatively short wavelength of 405 nm andan objective lens with a relatively large numerical aperture of 0.85.

First, it will be described why the thickness of the disk base materialto be the light transmitting layer is set equal to 0.1 mm. To reduce thesize of the light spot in writing data of about 23 GB, this optical diskdrive uses a laser beam with a wavelength of 405 nm and an objectivelens with as high a numerical aperture as 0.85. However, if thenumerical aperture of the objective lens is increased, then theresultant coma aberration also increases with respect to the tilt of thedisk. The coma aberration is proportional to the third power of thenumerical aperture of the objective lens. Accordingly, compared to asituation where a conventional objective lens with a numerical apertureof 0.6 is used, the coma aberration is about 2.8 times greater. Toeliminate such an unwanted increase in coma aberration, the phenomenonthat the coma aberration is proportional to the thickness of the basematerial may be utilized. In a DVD, the base material thickness is 0.6mm. Accordingly, it can be seen that a base material with a thickness of0.2 mm or less may be used. In this embodiment, a base material with athickness of 0.1 mm is used. As a result, a greater tilt is allowed forthe disk than the conventional DVD.

The diameter of the disk is set equal to 120 mm because the followingadvantage should be brought about. Specifically, since the CD and theDVD currently available both have a size of 120 mm, the user, who shouldbe used to the handiness or the ease of use of the CD and the DVD, wouldaccept a disk of the same size without feeling any inconvenience.

Next, it will be described why the data recording area is defined so asto extend from a radius of 24 mm to a radius of 58 mm. The innerboundary of the data recording area is defined by the inner radius of 24mm. This is done to make the drive (i.e., the optical disk drive)designable easily by adopting the same design parameter as theconventional DVD. Also, if the light transmitting layer is formed by aninjection molding process, for example, then the birefringence increasessteeply around the disk outer periphery. When the birefringence is somuch great, the amplitude of the read signal decreases and the datacannot be read accurately. For that reason, the outer boundary of thedata recording area is defined by 58 mm, inside which the birefringenceis relatively stabilized.

Next, it will be described why the land/groove recording technique isadopted. The land/groove recording technique is a method of recording asignal not only on groove tracks but also on land tracks between thegroove tracks. To write data of about 23 GB on an optical disk havingthe above-specified sizes, a disk having a very narrow groove pitchshould be made. In contrast, where the land/groove recording techniqueis adopted as is done in this embodiment, data is also written on thelands, and therefore, the groove pitch may be greater. Accordingly,there is no need to form grooves having a very narrow width and the diskcan be easily manufactured advantageously.

Next, it will be described why the track pitch (i.e., the distancebetween the center of a groove and that of an adjacent land) is setequal to 0.294 μm. As described above, to write data of about 23 GB,this optical disk drive uses a laser beam with a wavelength of about 405nm and an objective lens with a numerical aperture of about 0.85. In theconventional DVD-RAM on the other hand, a write operation is carried outunder the conditions including a laser wavelength of 660 nm and anumerical aperture of 0.6. As for the conventional DVD-RAM, a trackpitch of 0.615 μm was realized.

In this case, considering that the light spot diameter decreasesproportionally to the laser wavelength and inversely proportionally tothe numerical aperture of the objective lens, it can be seen that theoptical disk 1 of this embodiment can have a track pitch of 0.266 μm.

In the land/groove recording, however, the effects of a “cross-erase”phenomenon that a signal corresponding to an adjacent track happens tobe erased due to the thermal diffusion occurring during a writeoperation need to be taken into account. This is because there is justone physical level difference, contributing to the suppression ofthermal diffusion, between a land portion and a groove portion. Inrecording information only on the grooves on the other hand, there aretwo physical level differences between two grooves, i.e., a leveldifference between one groove and a land and a level difference betweenthe land and the other groove, and therefore, the thermal diffusion issuppressible relatively easily.

Considering that the light spot diameter may increase due to a variationof about 10 nm in laser wavelength and/or a variation of about 0.01 innumerical aperture, the track pitch required is 0.276 μm. Accordingly,by setting the track pitch equal to 0.28 μm or more, the resultantperformance will be comparable to that of the conventional DVD-RAM evenin view of possible variations of the optical system. It should benoted, however, that if the track pitch is greater than 0.32 μm, thedesired storage capacity cannot be obtained unless the data bit lengthis defined to be very short. Nevertheless, such a short data bit lengthis inappropriate because the read signal should increase its jitter inthat case. Thus, the track pitch is preferably 0.28 μm or more but 0.32μm or less. For these reasons, the optical disk of this embodiment has atrack pitch of 0.294 μm.

Next, it will be described why the data efficiency is set equal to83.7%. The “data efficiency” (also called “format efficiency”) is aratio of the user data capacity (i.e., the data capacity that can beused by the user) to the total data capacity. In this embodiment, a dataefficiency of as high as 80% or more is realized by adopting anappropriate data recording format. Hereinafter, this point will bedescribed in further detail.

For the conventional DVD-RAM, a format, in which 370 bytes of ECC (errorcorrection code) data and 279 bytes of address data, synchronizationdata and other types of data are added to every 2048 bytes of user data,has been adopted. In this case, the data efficiency is about 75.9%.

On the other hand, by adopting a format in which 279 bytes of addressdata, synchronization data and other types of data are added to every 16user data/ECC data sets, each consisting of 2048 bytes of user data and370 bytes of ECC data (i.e., to every 2418×16 bytes), the dataefficiency can be increased to about 84%. In the DVD-RAM, the ECC datais calculated for every 16 user data sets (i.e., 2048×1 6). Accordingly,if the address data and synchronization data are provided for every 16sets, these two groups of data can be well matched with each other.

Such a format in which the ratio of the address data to the user data isdecreased from the conventional one as described above is described inJapanese Patent Application No. 2000-014494, which was filed by theapplicant of the present application and which is hereby incorporated byreference. In that format, the address data (typically represented bypre-pits), which has been associated with each sector, is distributed inmultiple sectors. In this manner, a redundant portion of the addressdata can be eliminated from each of those sectors and the ratio of theaddress data capacity to the total capacity of an optical disk can bedecreased. In this embodiment, by using such a technique, a format, inwhich 370 bytes of ECC data, 4 bytes of address data, 26 bytes ofsynchronization data and other types of data are added to every 2048bytes of user data, is adopted, thereby obtaining a data efficiency of83.7%.

Also, where the address data is allocated dispersively to multiplesectors as described above, the pre-pits representing the address datamay have mutually different lengths. Such a technique is described inJapanese Patent Application No. 2001-034914, which was filed by theapplicant of the present application and which is hereby incorporated byreference.

In this manner, the data efficiency can be increased to 80% or morerelatively easily. By increasing the data efficiency, a greater mark canbe recorded. As a result, the read signal can have its amplitudeincreased and its quality improved.

Next, the data bit length will be described. The data bit length isdetermined with the track pitch, data efficiency, data recording areaand required user data capacity taken into account. In the example shownin Table 1, a user data capacity of 25 GB is achievable by setting thedata bit length equal to 0.1213 μm.

Next, it will be described why a modulation code of a 3T system (i.e., amodulation code in which the shortest mark length is three times as longas the channel bit length T) is adopted. Two types of modulation codeshaving shortest mark lengths of 2T and 3T, respectively, are known asbeing normally used for an optical disk or a magnetic disk. Examples ofthe former type that are used most frequently include a (1, 7, 2, 3)code (i.e., a so-called (1, 7) code). On the other hand, examples of thelatter type include a (2, 10, 8, 16) code (i.e., a so-called “8-16code”) for a DVD, for example. Each of these two types of modulationcodes has its own merits and demerits. Specifically, the (1, 7) code hasa short channel byte length of 12 bits and ensures good conversionefficiency, but the shortest mark length thereof is as short as 2T. Onthe other hand, the 8-16 code has a shortest mark length of 3T, which islonger than that of the (1, 7) code, but the channel byte length thereofis 16 bits, thus resulting in bad conversion efficiency.

The present inventors researched what difference is made by these twotypes of modulation codes in writing data of 25 GB or more. The resultsare shown in FIG. 3. FIG. 3 shows relationships between the recordingdensity (i.e., disk capacity) and the jitter of the read signal. Asshown in FIG. 3, in a range where the storage capacity is 24 GB or less,the (1, 7) code (of the 2T system) results in the smaller jitter. Thisis believed to be because this code ensures high conversion efficiency(i.e., one channel window width thereof is broader than that of the 8-16code). At densities of 24 GB or more, however, the relationship betweenthese two codes turns over. That is to say, the jitter caused by the (1,7) code worsens significantly. The reason is believed to be as follows.Since the shortest mark of the (1, 7) code is as short as 2T, the SNR ofthe mark declines extremely, thus affecting the signal jitterconsiderably. Accordingly, to reduce the jitter of the read signal, the8-16 code of the 3T system is the more advantageous at capacities of 25GB or more.

FIG. 4 shows relationships between the recording density (i.e., diskcapacity) and the bit error rate. As for this characteristic, thepresent inventors discovered that the relationship between the two typesof codes turns over at around 22 GB and that the bit error rate of the8-16 code is smaller than that of the (1, 7) code by more than one orderof magnitude at densities of 25 GB or more.

Based on the results described above, the present inventors discoveredthat to realize a recording density of 25 GB or more, the modulationcode of the 3T system is the more advantageous in terms of jitter andbit error rate. An 8-15 modulation code, ensuring higher efficiency byincreasing the channel bit length to 15 bits, is a typical non-8-16modulation code of the 3T system.

Next, it will be described why a so-called “product code (PC)”,represented as RS (208, 192, 17)×RS (182, 172, 11), is used as the errorcorrection code (ECC). Examples of error correction codes suitablyapplicable to an optical disk or a magnetic disk include not only theproduct code but also a long distance code (LDC) represented as (304)×RS(248, 216, 33). As in the modulation codes described above, the presentinventors carried out a similar research to determine which of these twoerror correction codes is more qualified to write data of 25 GB.However, it is not an effective measure to take to rate the qualities ofthese error correction codes by the data capacity (recording density).

The reason is as follows. Specifically, as the capacity is increased,the errors occur more and more often as shown in FIG. 4. However, thoseerrors are mostly random errors. The correction of those random errorsis certainly one of the purposes for which error correction processingis carried out. But the point is how much ability to correct bursterrors, generated by dust or dirt attached to the disk surface, theerror correction processing has. Thus, the present inventors obtained,through computation, the relationships between the average burst lengthof the errors and the error correcting ability for these two types oferror correction codes. The results are shown in FIG. 5.

In FIG. 5, the abscissa represents the average burst error length. Atany average burst error length, the total symbol error rate is supposedto be 2×1 0−2. The ordinate represents the percentage of uncorrectableerrors, which is the percentage of errors remaining even after the errorcorrection processing has been carried out. As can be clearly seen fromFIG. 5, the relationship between the two types of error correction codesturns over at an average burst length of about 30-40 bytes. That is tosay, if the burst length is longer than that value, the LDC results inthe lower uncorrectable error percentage and realizes more appropriatecorrection. However, if the burst errors are short, then the PC showshigher correcting ability (i.e., lower uncorrectable error percentage)than the LDC. It should be noted that to obtain the results shown inFIG. 5 through computation, the PC is subjected in advance to a diagonalinterleaving processing such as that shown in FIG. 6.

The “diagonal interleaving processing” herein refers to the followingtype of processing. First, two PCs stored on a memory are subjected tointerleaving processing, thereby forming two PC groups. Next, each ofthese PC groups formed is read diagonally, e.g., a symbol at the 2ndrow, 2nd column is read after a symbol at the 1st row, 1st column hasbeen read. Thereafter, those symbols of the PCs are recorded on the diskin the order in which those symbols have been read. Then, the PC canexhibit correcting ability that has been strengthened against bursterrors. It should be noted that such diagonal interleaving processing isdescribed in Japanese Patent Application No. 2000-317452, for example,which was filed by the applicant of the present application and which ishereby incorporated by reference.

In this case, the question is exactly how big the dirt actually attachedto an optical disk is. As for an optical disk packaged in a cartridge,it is expected that only dust or dirt that is small enough to passthrough the gap of the cartridge can be attached to the disk. Forexample, the smoke particles of a cigarette have a diameter of at mostabout 10 μm. As described above, supposing one data bit length is equalto about 0.12 μm, one data byte length is eight time longer, i.e., about1 μm. Accordingly, the cigarette smoke particle size of 10 μm may beregarded as corresponding to about 10 bytes. Thus, considering the bursterrors caused by those fine particles that are small enough to enter thecartridge, it is expected that the product code should exhibit thehigher correcting ability.

As described above, the optical disk according to the first embodimentof the present invention has a track pitch of 0.294 μm and a data bitlength of 0.1213 μm, thus realizing a track density that is allowed asufficient margin against the cross-erase phenomenon even in view ofpossible variations of the optical system. Also, by adopting amodulation code having the shortest mark length of 3T (e.g., 8-16modulation code), the jitter can be kept smaller than a code of the 2Tsystem (e.g., (1, 7) code) at recording densities of 24 GB or more.Furthermore, by using an error correction code represented as RS (208,192, 17)×R S (182, 172, 11) (i.e., the product code), the short bursterrors, caused by the dust that has been attached to the disk surface,can be corrected effectively. As a result, an optical disk having apractical capacity of 25 GB can be provided.

As for the embodiment described above, an optical disk including spiralgrooves thereon has been described. Alternatively, the optical disk mayinclude concentric grooves and lands thereon.

Embodiment 2

FIGS. 7(a) and 7(b) are respectively a perspective view and a partialview of an optical disk 11 according to a second embodiment of thepresent invention.

As shown in FIG. 7(a), spiral grooves 12 have been formed on the opticaldisk 11. This optical disk 11 has a diameter of 120 mm and has beenformed to have a total thickness of 1.2 mm. Also, as shown in FIG. 7(b),the optical disk 11 is made by forming an information recording layer 14of a GeSbTe film, for example, on a disk substrate 13. A lighttransmitting layer 15, which transmits a laser beam and guides it ontothe information recording layer 14, is further formed on thisinformation recording layer 14 so as to have a thickness of about 0.1mm. A zone between two grooves 12 is also called a land 16. In theoptical disk 11 of this embodiment, however, data is recorded either onthe grooves 12 or on the lands 16.

The grooves are wobbled. The optical depth of the grooves is setapproximately equal to λ/12, where λ is the laser wavelength. This isdone to increase the amplitude of a signal and to obtain practicalpush-pull signal amplitude.

In recording data only on the grooves 12, the groove width is setgreater than the land width. On the other hand, in recording data onlyon the lands, the land width is set greater than the groove width. Inthat case, the signal amplitude can be increased and the signal qualitycan be improved.

The following Table 2 shows various parameters of the optical disk 11 ofthis embodiment, the wavelength of the laser beam for use to recordinformation on this optical disk, and the numerical aperture of theobjective lens for use to focus the laser beam onto the optical disk:

TABLE 2 Laser wavelength 405 nm Numerical aperture 0.85 Of objectivelens Thickness of 0.1 mm light transmitting layer Diameter of disk 120mm Data recording area 24-58 mm in radius Data efficiency 84.6%Recording method Groove recording (or land recording) Track pitch 0.32μm Data bit length 0.1155 μm Channel bit length (T) 0.0578 μm Shortestmark length 3T (0.1733 μm) Error correction code RS (208, 192, 17) × RS(182, 172, 11)

A base material with a thickness of 0.1 mm is used as the lighttransmitting layer because of the same reason as that described for thefirst embodiment. Also, the disk diameter is set equal to 120 mm and thedata recording area is defined to extend from a radius of 24 mm to aradius of 58 mm for the same reasons as those already described for thefirst embodiment.

Next, it will be described why the groove recording is adopted. Forexample, if the groove recording technique is applied to an opticaldisk, which uses a phase change type material so that an amorphousportion is formed as a recording mark and from which a difference inreflectance between the crystalline and amorphous portions is read as asignal, then the film thereof may be designed in such a manner as tocreate a phase difference between the amorphous and crystalline portionsand thereby obtain great amplitude. In the land/groove recordingtechnique, however, the difference in depth between the lands and thegrooves, i.e., the phase difference between them, is used to reduce thecrosstalk. Accordingly, such a design as to create a phase differencebetween the amorphous and crystalline portions is not preferable for theland/groove recording technique because the crosstalk increases in thatcase. Thus, by adopting the groove recording technique, the signalamplitude designed can be great and the signal quality can be improved.

Next, it will be described why the track pitch is set equal to 0.320 μm.As in the first embodiment, a laser beam with a wavelength of about 405nm and an objective lens with a numerical aperture of about 0.85 arealso used in this embodiment to write data of about 23 GB. Accordingly,as already described for the first embodiment, the track pitch can beset equal to 0.266 μm for a write operation.

In the groove recording technique, however, if the track pitch (i.e.,the distance between the center of a groove and that of an adjacentgroove) is 0.266 μm, the amplitude of a push-pull signal is small.Accordingly, a non-negligible variation should occur in the amplitude ofthe push-pull signal if the track pitch is not constant. As a result, itbecomes difficult to perform the tracking servo control.

FIG. 8 shows the results obtained by simulating the relationship betweenthe track pitch and the variation in amplitude of a push-pull signal dueto inconstant track pitches. The variation in track pitch was supposedto be ±5 nm, which is an adequate value that is actually realizable in amanufacturing process in view of the feeding precision of a cuttingmachine, for example. To realize a tracking servo system that worksstably, the amplitude variation is preferably 2 dB or less. For thatpurpose, the track pitch is preferably 0.32 μm or more.

Next, it will be described why the data efficiency is defined as 84.6%.The conventional DVD-RAM has a format in which 370 bytes of ECC data and279 bytes of address data, synchronization data and other types of dataare added to every 2048 bytes of user data. Thus, the data efficiencythereof was 75.9%. If this data efficiency can be increased, then agreater mark can be recorded and the read signal can have its amplitudeincreased and its quality improved.

For example, by replacing the format of the conventional DVD-RAM with aformat in which 279 bytes of address data, synchronization data andother types of data are added to every 16 user data/ECC data sets (i.e.,to every 2418×1 6 bytes), the data efficiency can be increased to about84%. In the DVD-RAM, the ECC data is calculated for every 16 user datasets (i.e., 2048×16). Accordingly, if the address data andsynchronization data are provided for every 16 sets, these two groups ofdata can be well matched with each other. In this manner, the dataefficiency can be increased to 80% or more relatively easily.

On the other hand, by adopting, as a format realizing higher dataefficiency, a format in which 93 bytes of block marks and so on areadded to every 32 user data/ECC data sets (i.e., to every 2418×32bytes), a data efficiency of 84.6% is realized in this embodiment. Inthe DVD-RAM, the ECC data is calculated for every 16 user data sets(i.e., 2048×16). Accordingly, if the block marks and so on are providedfor the double thereof, i.e., every 32 sets, these two groups of datacan be well matched with each other.

It should be noted that to achieve that high data efficiency, addressdata is represented in this embodiment by changing the wobble patternsof the grooves. Thus, areas for address data can be eliminated. Then,the areas that were allocated to the address data can also be used asuser data areas. As a result, the data efficiency can be increased. Thistechnique is described in Japanese Patent Application No. 2000-319009,which was filed by the applicant of the present application and which ishereby incorporated by reference.

Hereinafter, an optical disk, in which the wobbling structure of thetrack grooves is defined by a combination of several types ofdisplacement patterns, will be described in detail with reference to theaccompanying drawings.

In this embodiment, the planar shape of the track grooves does notconsist of just a sine waveform but at least part of it has a shapedifferent from the sine waveform. A basic configuration for such agroove is disclosed in the descriptions of Japanese Patent ApplicationsNos. 2000-6593, 2000-187259 and 2000-319009, which were filed by theapplicant of the present application and which are hereby incorporatedby reference.

FIG. 10(a) illustrates the four types of basic elements that make up awobble pattern of the track grooves 2. In FIG. 10(a), smooth sinewaveform portions 100 and 101, a portion 102 with a steepdisk-outer-periphery-oriented displacement and a portion 103 with asteep disk-inner-periphery-oriented displacement are illustrated. Bycombining these elements or portions with each other, the four types ofwobble patterns 104 through 107 shown in FIG. 10(b) are formed.

The wobble pattern 104 is a sine wave with no steeply displacedportions. This pattern will be herein referred to as a “fundamentalwaveform”. It should also be noted that the “sine wave” is not hereinlimited to a perfect sine curve, but may broadly refer to any smoothwobble.

The wobble pattern 105 includes portions that are displaced toward thedisk outer periphery more steeply than the sine waveform displacement.Such portions will be herein referred to as “outer-periphery-orienteddisplaced rectangular portions”.

In an actual optical disk, it is difficult to realize the displacementof track grooves in the disk radial direction vertically to the trackdirection. Accordingly, an edge actually formed is not perfectlyrectangular. Thus, in an actual optical disk, an edge of a rectangularportion may be displaced relatively steeply compared to a sine waveformportion and does not have to be perfectly rectangular. As can also beseen from FIG. 10(b), at a sine waveform portion, a displacement fromthe innermost periphery toward the outermost periphery is completed in ahalf wobble period. As for a rectangular portion, a similar displacementmay be finished in a quarter or less of one wobble period, for example.Then, the difference between these shapes is sufficiently detectible.

The wobble pattern 106 is characterized by inner-periphery-orienteddisplaced rectangles while the wobble pattern 107 is characterized byboth “inner-periphery-oriented displaced rectangles” and“outer-periphery-oriented displaced rectangles”.

The wobble pattern 104 consists of the fundamental waveform alone.Accordingly, the frequency components thereof are defined by a“fundamental frequency (or wobble frequency)” that is proportional tothe inverse number of the wobble period T. In contrast, the frequencycomponents of the other wobble patterns 105 through 107 include not onlythe fundamental frequency components but also high-frequency components.Those high-frequency components are generated by the steep displacementsat the rectangular portions of the wobble patterns.

In this embodiment, instead of writing address information on thegrooves 2 by modulating the wobble frequency, the multiple types ofwobble patterns are combined with each other, thereby recording varioustypes of information, including the address information, on the trackgrooves. More specifically, by allocating one of the four types ofwobble patterns 104 through 107 to each predetermined section of thetrack grooves, four types of codes (e.g., “B”, “S”, “0” and “1”, where“B” denotes block information, “S” denotes synchronization informationand a combination of zeros and ones represents address data, forexample) may be recorded.

Next, the fundamentals of an inventive method for reading information,which has been recorded by the wobble of the track grooves, from theoptical disk will be described with reference to FIGS. 11 and 12.

FIG. 11 illustrates a main portion of a reproducing apparatus. The trackgroove 1200 schematically illustrated in FIG. 12 is scanned by a readlaser beam 1201 so that the spot thereof moves in the directionindicated by the arrow. The laser beam 1201 is reflected from theoptical disk to form reflected light 1202, which is received bydetectors 1203 and 1204 of the reproducing apparatus shown in FIG. 11.The detectors 1203 and 1204 are spaced apart from each other in adirection corresponding to the disk radial direction and each output avoltage corresponding to the intensity of the light received. If theposition at which the detectors 1203 and 1204 are irradiated with thereflected light 1202 (i.e., the position at which the light is received)shifts toward one of the detectors 1203 and 1204 with respect to thecenterline that separates the detectors 1203 and 1204 from each other,then a difference is created between the outputs of the detectors 1203and 1204 (which is “differential push-pull detection”). The outputs ofthe detectors 1203 and 1204 are input to a differential circuit 1205,where a subtraction is carried out on them. As a result, a signalrepresenting the wobble shape of the groove 1200 (i.e., a wobble signal1206) is obtained. The wobble signal 1206 is input to, anddifferentiated by, a high-pass filter (HPF) 1207. Consequently, thesmooth fundamental components that have been included in the wobblesignal 1206 are attenuated and instead a pulse signal 1208, includingpulse components corresponding to rectangular portions with steepsgradients, is obtained. As can be seen from FIG. 12, the polarity ofeach pulse in the pulse signal 1208 depends on the direction of itsassociated steep displacement of the groove 1200. Accordingly, thewobble pattern of the groove 1200 is identifiable by the pulse signal1208.

Next, referring to FIG. 13, illustrated is an exemplary circuitconfiguration for generating the pulse signal 1208 and a clock signal1209 from the wobble signal 1206 shown in FIG. 12.

In the exemplary configuration illustrated in FIG. 13, the wobble signal1206 is input to first and second band-pass filters BPF1 and BPF2, whichgenerate the pulse and clock signals 1208 and 1209, respectively.

Supposing the wobble frequency of the track is fw (Hz), the firstband-pass filter BPF1 may be a filter having such a characteristic thatthe gain (i.e., transmittance) thereof reaches its peak at a frequencyof 4 fw to 6 fw (e.g., 5 fw). In a filter like this, the gain thereofpreferably increases at a rate of 20 dB/dec, for example, in a rangefrom low frequencies to the peak frequency, and then preferablydecreases steeply (e.g., at a rate of 60 dB/dec) in a frequency bandexceeding the peak frequency. In this manner, the first band-pass filterBPF1 can appropriately generate the pulse signal 1208, representing therectangularly changing portions of the track wobble, from the wobblesignal 1206.

On the other hand, the second band-pass filter BPF2 has such a filteringcharacteristic that the gain thereof is high in a predeterminedfrequency band (e.g., in a band ranging from 0.5 fw to 1.5 fw andincluding the wobble frequency fw at the center) but is small at theother frequencies. The second band-pass filter BPF2 like this cangenerate a sine wave signal, having a frequency corresponding to thewobble frequency of the track, as the clock signal 209.

Next, the data bit length will be described. The data bit length isdetermined with the track pitch, data efficiency, data recording areaand required user data capacity taken into account. In the example shownin Table 2, a user data capacity of 25 GB is achievable by setting thedata bit length equal to 0.1155 μm.

It should be noted that the reason why a modulation code of the 3Tsystem is used and the reason why a so-called product code (PC),represented as RS (208, 192, 17)×RS (182, 172, 11), is used as the errorcorrection code are the same as those already described for the firstembodiment.

As described above, the disk drive according to the second embodiment ofthe present invention adopts a track pitch of 0.32 μm and a data bitlength of 0.1155 μm, thereby achieving the maximum track density withina range in which the tracking error signal is detectible. Also, byadopting a modulation code having the shortest mark length of 3T (e.g.,8-16 code), the jitter can be kept smaller than a code of the 2T system(e.g., (1, 7) code) at recording densities of 24 GB or more.Furthermore, by using an error correction code represented as RS ((208,192, 17)×RS (182, 172, 11), the short burst errors, caused by the dustthat has been attached to the disk surface, can be correctedeffectively. As a result, an optical disk having a practical capacity of25 GB can be provided.

As for the embodiment described above, an optical disk including spiralgrooves thereon has been described. Alternatively, the optical disk mayinclude concentric grooves and lands thereon.

Embodiment 3

Hereinafter, an optical disk according to a third embodiment will bedescribed. This optical disk has the same configuration as the opticaldisk of the first embodiment shown in FIG. 1. However, unlike the firstembodiment, modulation is carried out by using a modulation code of the2T system.

The following Table 3 shows various parameters of the optical disk ofthis embodiment, the wavelength of the laser beam for use to recordinformation on this optical disk, and the numerical aperture of theobjective lens for use to focus the laser beam on the optical disk:

TABLE 3 Laser wavelength 405 nm Numerical aperture 0.85 of objectivelens Thickness of 0.1 mm light transmitting layer Diameter of disk 120mm Data recording area 24-58 mm in radius Data efficiency 83.7%Recording method Land/groove recording Track pitch 0.294 μm Data bitlength 0.1213 μm Channel bit length (T) 0.0809 μm Shortest mark length2T (0.1617 μm) Error correction code RS (208, 192, 17) × RS (182, 172,11)

A base material with a thickness of 0.1 mm is used as the lighttransmitting layer because of the same reason as that described for thefirst embodiment. Also, the disk diameter is set equal to 120 mm, thedata recording area is defined to extend from a radius of 24 mm to aradius of 58 mm and the land/groove recording technique is adopted forthe same reasons as those already described for the first embodiment.

In this embodiment, however, a modulation code of the 2T system is used.The reason will be described below.

In using a modulation code of the 2T system, if the data bit length isthe same, the channel bit length increases compared to the 3T system.Accordingly, the 2T system needs a lower channel clock frequency toachieve the same data transfer rate. Thus, when the transfer rate ishigh, it is more preferable to use a modulation code of the 2T system.

More specifically, supposing the data transfer rate is T (megabits persecond) in the example shown in Table 3, the 2T system (e.g., (1, 7)modulation) needs a channel clock frequency of 1.5 T (MHz) while the 3Tsystem (e.g., (8-16) modulation) needs a channel clock frequency of 2.0T (MHz)

In using a modulation code of the 2T system, however, the shortest marklength is shorter than that of the 3T system, and a 2T mark has smallsignal amplitude, thus possibly deteriorating the jitterdisadvantageously. In that case, a 2T mark is easily detected as a 1Tmark erroneously. As a result, errors may occur.

Nevertheless, in decoding a signal by a PRML (partial response maximumlikelihood) method, a most likely signal is estimated by performingpattern matching on the signal, and therefore, even a signal containingan error may be decoded correctly. In this case, even if a 2T mark hasbeen detected as a 1T mark erroneously, the 2T mark can also be decodedcorrectly by the PRML decoding method.

FIGS. 9(a) and 9(b) show how the jitter and the bit error rate of a readsignal change with the tilt angle in the PRML reading method when theshortest mark length is 0.138 μm. In FIGS. 9(a) and 9(b), the abscissasrepresent a tilt angle in the tangential direction (i.e., a tangentialtilt) and a tilt angle in the radial direction (i.e., a radial tilt),respectively.

As can be seen from these drawings, since the mark length is as short as0.138 μm, the jitter is as high as 15%. However, even when the jitter isthat high, the bit error rate after the mark has been decoded by thePRML reading method is 1033 e −4, which is good enough.

Thus, in decoding a mark by the PRML method, even if a modulation codeof the 2T system is used, the occurrence of errors is minimized andtherefore no problems should be caused.

Also, as shown in FIG. 9, if a signal is read by the PRML reading methodwhen a modulation code of the 2T system is used, high read signalquality is still ensured even though the shortest mark length is 0.138μm. Accordingly, where the shortest mark length is set equal to 0.138μm, a track pitch realizing a capacity of 25 GB may be increased to atleast 0.344 μm.

Embodiment 4

Hereinafter, an optical disk according to a fourth embodiment will bedescribed. This optical disk has the same configuration as the opticaldisk 11 of the second embodiment shown in FIG. 7. However, unlike thesecond embodiment, a modulation code of the 2T system is used.

The following Table 4 shows various parameters of the optical disk ofthis embodiment, the wavelength of the laser beam for use to recordinformation on this optical disk, and the numerical aperture of theobjective lens for use to focus the laser beam on the optical disk:

TABLE 4 Laser wavelength 405 nm Numerical aperture 0.85 of objectivelens Thickness of 0.1 mm light transmitting layer Diameter of disk 120mm Data recording area 24-58 mm in radius Data efficiency 84.6%Recording method Groove recording Track pitch 0.32 μm Data bit length0.1155 μm Channel bit length (T) 0.077 μm Shortest mark length 2T (0.154μm) Error correction code RS (208, 192, 17) × RS (182, 172, 11)

A base material with a thickness of 0.1 mm is used as the lighttransmitting layer because of the same reason as that described for thesecond embodiment. Also, the disk diameter is set equal to 120 mm, thedata recording area is defined to extend from a radius of 24 mm to aradius of 58 mm and the groove recording technique is adopted for thesame reasons as those already described for the second embodiment.

In this embodiment, however, a modulation code of the 2T system is used.Even so, by combining the 2T modulation code with the PRML readingmethod as described for the third embodiment, the error rate can bereduced. Also, since the channel clock frequency becomes relatively low,this modulation effectively contributes to achieving a high transferrate.

In the optical disk of this embodiment, when the shortest mark lengthwas set equal to 0.138 μm, the same results as those shown in FIGS. 9(a)and 9(b) were also obtained. Accordingly, where the shortest mark lengthis set equal to 0.138 μm, a track pitch realizing a capacity of 25 GBmay be increased to at least 0.357 μm.

INDUSTRIAL APPLICABILITY

The present invention provides an optical disk having high storagecapacity by increasing the recording density greatly. For example, anoptical disk having a diameter of 120 mm and a storage capacity of 23 GBor more, for example, is realized by the present invention.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

We claim:
 1. An optical disk which comprises a land and a groove and onwhich data is recorded on both the land and the groove, wherein adistance between the center of the land and the center of the grooveadjacent to the land is 0.28 μm or more, wherein a product code is usedas an error correction code, wherein the groove comprises a plurality ofwobble patterns representing address information, and wherein theoptical disk has a data efficiency of 80% or more, said data efficiencybeing defined by a ratio of a user data capacity that can be used by auser to a total data capacity of the optical disk.
 2. The optical diskof claim 1, wherein the data is recorded by using a modulation code of a3T system.
 3. The optical disk of claim 1, wherein the data is recordedby using a modulation code of a 2T system.
 4. The optical disk of claim1, further comprising a light transmitting layer on the surface of thedisk on which the groove and the land have been formed, wherein thelight transmitting layer has a thickness of 0.2 mm or less.
 5. Anoptical disk which comprises a land and a groove and on which data isrecorded on either the land or the groove, wherein a pitch of the grooveand a pitch of the land are 0.32 μm or more, wherein a product code isused as an error correction code, wherein the groove comprises aplurality of wobble patterns representing address information, andwherein the optical disk has a data efficiency of 80% or more, said dataefficiency being defined by a ratio of a user data capacity that can beused by a user to a total data capacity of the optical disk.
 6. Theoptical disk of claim 5, wherein the data is recorded by using amodulation code of a 3T system.
 7. The optical disk of claim 5, whereinthe data is recorded by using a modulation code of a 2T system.
 8. Theoptical disk of claim 5, further comprising a light transmitting layeron the surface of the disk on which the groove and the land have beenformed, wherein the light transmitting layer has a thickness of 0.2 mmor less.
 9. The optical disk of claim 1, wherein the optical disk has astorage capacity of 23 GB or more.
 10. The optical disk of claim 1,wherein the optical disk further comprises a recording layer of a phasechange material and the data is rewritable.